Two New Zealand women being sued $20,000 by an Israeli law firm, due to the cancellation of a Lorde concert, say the claim is “delusional.”

This week, law firm Shurat HaDin announced it would sue Justine Sachs and Nadia Abu-Shanab for an open letter they wrote to Lorde urging the performer to boycott Israel and cancel her concert in Tel Aviv.

The firm’s founder, Nitsana Darshan-Leitner, said Shurat HaDin was suing for about $20,000 on behalf of three 17-year-old Israeli women who had suffered “mental harm” due to the cancellation.

But this morning, Abu-Shanab - who is a teacher, unionist, and Palestine activist - dismissed the lawsuit as a bullying tactic.

She said she and Sachs, who is a Jewish freelance writer, grad student and activist, had not received a summons.

“At this point it’s not serious or formal legal action, and that's where we’re standing on it,” she told RNZ.

“But the people who are doing this are deadly serious, which is the worrying thing. It sounds delusional - and it is delusional from our perspective - but they’re very serious in their line of belief that they can squash free speech. I think that’s probably the concerning point for people.”

The pair said the idea that an open letter they wrote to Lorde last year was the sole reason for the cancellation of the Tel Aviv show was laughable.

“We wrote an open letter joining hundreds of thousands of people calling on her to cancel and the decision was ultimately hers.

“For us to take credit for that would be an act of supreme arrogance… We were just one of many voices.”

In a 2015 profile, the New York Times described Darshan-Leitner of Shurat HaDin as “a crusading lawyer who serially sues rogue nations, terror groups and international banks to show, as she put it, “there is a price to Jewish blood.”

The Times reported that about 90 percent of the $US1.6 billion in default judgements against countries like Iran and Syria, who did not show up to defend the claims against them, had not been paid.

“What happens in the end doesn’t affect your mission,” she said. “If we win the money, it will be great, but this is not the reason we’re going to court.”

Sachs and Abu-Shanab said they would not be told what to say.

"Instead of scaring us, these bullying tactics [by Shurat HaDin] only embolden us and make it self-evident that there is a right and wrong in this situation. We are proud to stand for what is right."